Hot top



Aug. 12, 1958 n. D. wHrrAcRE HOT TOP File-d NOV. 2, 1954 INVENTOR. ,DO/VAL D .D- WH/ TACEE ATTORNEYS ik! El United States Patent O HOT TOP Donald D. Whitacre, Waynesburg, Ohio, assignor to The Whitacre-Greer Fireprooling Company, Waynesburg, Ohio, a corporation of Ohio Application November 2, 1954, Serial No. 466,326

3 Claims. (Cl. 22-147) This invention relates to hot tops for ingot molds and more particularly to improvements in ceramic or refractory hot tops through which the yield and quality of ingots cast therewith may be increased and enhanced.

An object of my invention is to provide a hot top by the use of which segregation-free alloy steel ingots may be cast witha crop of no more than 10%; an objective long sought but not achieved prior to my invention. A general object of my invention is to improve upon the art and the hot top described and disclosed in the Estep Patent No. 2,159,374 and to solve the problems recognized in and remaining unsolved by the teaching thereof. Another object of my invention is to provide a ceramic hot top of separable parts of dierent functional characteristics wherewith each part can be made to play its role to greatest advantage in the whole unitary structure, function, operation and result of complete product. Other objects include the provision of a hot top that may be economically manufactured, transported and used; and that has such mechanical strength and thermal properties as to insure the successful and enhanced casting of segregation-free ingots without piping and with the savings and advantages of the novel small crop mentioned above.

A specific object is to provide a hot top and practice of casting ingots so improved over and upon the teaching of the George A. Bole et al. application Serial No. 240,676, led August 7, 1951, now abandoned, that the desirable and avowed objects and intentions of that application may in fact be achieved.

Other objects and advantages of my invention will appear from the following description of a preferred form and practice thereof; reference being had to the accompanying drawings in which:

Figure l is an exploded perspective View of the sleeve and collar parts of my hot top axially aligned and spaced prior to assembly;

Figure 2 is a top plan view of my assembled hot top;

Fig. 3 is a side elevation of my assembled hot top;

Figure 4 is a composite longitudinal section showing my hot top in operative relation to the upper end of an ingot mold with a rst stage of pouring the ingot suggested in the left half of the ligure and the final stage of pouring the ingot and lling the hot top suggested in the right half of the ligure;

Figure 5 s a fragmentary enlarged longitudinal section of a bottom portion of my assembled hot top showing a seal between the lower parts thereof.

In the preferred form of my invention herein particularly illustrated and described, the assembled hot top H, Figures 2 and 3, comprises the sleeve or sleeve part S and the collar or collar part C, see Figure l, the former having its lower end telescopically nested within the latter, see Figure 4, resting thereon and attached and secured thereto, whereby to be employed as a unit and disposed on and within the brim of a big-end-up mold M ICC to perform its intended service in aid of casting the ingot I.

In this preferred form of my invention, the sleeve S takes substantially right, not necessarily circular, hollow cylindrical form and-has a thick annular wall characterized by its high uniformly line porosity, low density, low heat capacity, low thermal transmittance, low specific heat, necessary mechanical strength and resistance to spalling, whereby to embrace the crop K (first in the liquid state as suggested in the right half of Figure 4) and keep it, or the last increment thereof to solidify, hot and fluid for such a long period of time in relation to the solidiiication of the body of the ingot I that the ingot shall be free of piping and segregation, and the linal solidified-crop lwith its voids and impurities shall comprise less than 1A() the mass of the whole ingot and crop.

The collar C serves to support the sleeve S, fit the interior of the brim of mold externally, t the exterior of the lower part of the sleeve S internally, `anchor and locate the hot top as a whole in its proper relation to the mold and ingot, afford a major element of structural vstrength for the whole hot top, and is characterized by yits strength and higher density and higher heat capacity than the sleeve S. Inter alia, the collar C functions to seal the molten steel from egress between its exterior and the brim of the mold; lirst making the seal whilst the level L of molten steel is approximately as shown at the left in Fig. 4, and by virtue of its higher heat capacity functions to freeze the molten steel around or adjacent its lowermost end and/or between its lowermost end and the adjacent surface of the mold and become substantially bonded or vanchored to the upper and outerrst frozen crust of the ingot whereby to resist the tendency of the hot top as a whole, and particularly with the low density sleeve S, to float or rise upwardly when the hot top is iirst lled with molten steel to the level -L as suggested in the right half of Fig. 4.

I prefer to make the sleeve S by longitudinal extrusion, familiar in the manufacture of clay products, of a mixture (wetted for extrusion) of about equalparts by volume of clay, preferably good tire clay, and anthracite silt to which is added up to about 20% sawdust or pulver'- ized bituminous coke of 'about the mesh of sawdust. Al-

ternatively, the sawdust and/or coke may be omitted entirely. Alternatively, I have also found it practicable l to use amixture of about 40% to 50% clay and about 60% to 50% anthracite silt. Within these ranges of mixtures, after the sleeve has been formed and dried,` it is burned until all or substantially all the carbonaceous material has been consumed and burned out leaving a strong, highly porous, minutely voided (perhaps it could be called minutely honeycombed) wall structure of accurately predictable, controllable and uniform density, insulating value and heat capacity `and with a smooth nonspalling skin or surface and with predictable-and controllable form and dimension. I have found advantage in reducing the clay content of the mixture below 1/z and in employing a slow burning of the Ware at between about 1400 F.-1600 F. Thatis to say, while I have made many successful hot top sleeves within the present invention with a mixture of equal parts of clay and anthracite silt, the burning time, with Wall thicknesses of between 2%-3, may be as much as three weeks to effect the Whole combustion of all the carbonaceous material and the development of the uniformly and minutely voided structure that I desire. When the 'proportion ofanthracite silt alone to clay is increased, as'to 60-40, `the burning time is desirably reduced without deleterious pairment of desirable qualities, such as structural strength, resistance to thermal shock and spalling, while' the desir'-- able-density, insulating value and Aheat capacity is `preserved and/or improved. When, as I presently prefer, a mix of 40% clay, 40% anthracite silt and 20% sawdust or granulated-cokeis-employed,'the 'desirable qualities are preserved and enhanced and the burning time for-complete combustion of-all-the carbonaceouscontent at vabout the burning Vtemperatures mentioned above is reduced Ito about x1/thatrequired for 'the 5 0-"50 mixture -of anthracite silt-andclay. 'These examples are-stated for'illustr-atonof principles 'upon -which other variants may be enjoyed. Within these lprinciples my present 4observation and understanding suggests: The `proportion 'of -clay to cornbustibles measures the ultimate essential `workingstructural content ofthe -burned 'ware throughwhich the meehanical *and Ethermal -virtues and value are obtained, regard being-had fortthefstrength and thermal :values arising-from'the'porous or-minutehoneycomb structure and the #tiring of `Athe vast `surfaces `thereof vby the correct burning of the ware, including the burning yof `the ware by the combustible content. The proportion of anthracite 'siltffunctions to give -the fne porosity with -low ash content Aand advantageous burning of the walls and wall"surfaces lof the pores. The proportion of sawdust or-granularbituminous coke tends to lburn out ahead'of and/or -infencouragement of the burning ofthe anthracite silt and `probably Iintersperses Alargersmall voids or pores throughout `the primary minute porous structure, and lreduces fburning time, vprobably by making it easier for 'oxygen to-get to the silt orotherwise promote combus'tionof the silt in the smaller voids or pores in the middle'of 'the -wall structure. The net ash residuum of sawdust 'or coke -is small in relation `to the initial volume; wet sawdust for'example having a high volume `in the Wet extruded ware relative 1to the ash thereof in the finished ware. For general guidance, at the expense of oversimpliflcation, I aim -to provide and retain in the sleeve 'S the benecent qualities and characteristics obtained twiththe fully `burned'out 50-50 -mixture of good fire-'clay andanthracite Isilt and I seek to illustrate by principle and example wherein and lhowthe substance or substantial equivalents of -those `beneticcnt qualities and characteristicscanibe rpreserved or not deleteriously-impaired while gaining other 'desirable advantages.

I lprefer anthracite silt forthe major combustible constituent of the pre-extruded and pre-burned mixture because `it Aworks-easilyin extrusion, -has a low ash content when-"burnedin, i. e. out'of the ware, is relatively inexpensivefdoes not shorten the ware adversely -and is readily and .naturally obtainable yin finely -divided `form, havingfpreferably 'the neness of our or'talcum powder. By shortening, `I-mean that combustibles with high Vash content ltend Vto -make Vtheware more friable. `Wheat'iiour and substantially equally ine'ly divided petroleum coke have -properties substantially similar to anthracite silt for'the 'purposes of my invention, regard beinglhad for cost as the same may be alected by price ator'near the place of `manufacture -of the -hot tops. The restrained use fof lsawdustand granular bituminous coke AWithin the 'limits presently suggested has -not been found to shorten the wareadversely, butif adverseshortening appears ffrom particular-sawdustsor'bituminous cokes or from testing =oraexceeding :the upper-limits of the proportions'thereofthat'l prefer, then the substitution of coarsely'fdividedfaspf about-the iinenessof sawdust or commonrgranulated table salt or sugar) petroleum coke for all or yparto'fithe sawdust-or'bituminous coke will, pro tanto, 1relieve-oreliminate the adverse shortening `of the ware. 'These particular combustibles and their properties-13nd functions :in the practice of my invention are cited iforfexamples and :illustration rather than 4limitation.

'The-.sleevetS produced WithrtheSO-SO clay andI anthracite-siltmix and thelong even-burning lmentioned above has a uniform density of about 0.65 to 0.68 ounce per cubicinch, compared with adensityof about 1.2 to 41.25 ounces per cubic inch or more for a product of the same clay produced without any initial carbonaceous content. The wall of the sleeve S made of the 50-50 mix, if about 21/2 thick, has an insulating value such that under steady heat conditions with the ,hot side maintained at about 1000 F., the cold side will not substantially exceed about 200 F., i. e. at a gradient of about 320 F. per inch. -Heat capacity approximately follows density. When the clay contentof -themixis reduced as described above, the density is correspondingly, but not necessarily proportionately, reduced, regard being vhad for shrinkage in burning, and the insulating value correspondingly and similarly enhanced. While I have given below a specific example of the dimensions and proportions of a hot top embodying my invention for use with a particular ingot mold, Vmy understanding yand .teaching .about arriving at the best wall .thickness .for the sleeve Sispresently this: Primarily :the oce -of the sleeve ,is to delay solidication of tthe uid metal crop inthe .feedopening `until after :the ingot has solidified, the `latterbeing a determinable, substantially direct function of the diameter of the ingot adjacentthe hot.top. As is `understood in the art the diameter of a square .mold is taken approximatelyequal the side -,of .the square. The sleeve S therefore .works against different times for .larger and smaller ingots and the etciency of ythe sleeve may `be measured ,in terms ofhow little heat it takes .from and ,allows to flow from the crop before the ingot solidifies. The advantage `oflow heat capacitytin `the sleeve is that little heat is taken -from the crop to heat the sleeve, so that this consideration alone speaks ,for-a Ithinner and lessdensewall yfor the sleeve. On .the other hand, Vtotal insulating value lconsidered alone speaks `'for a `thicker walled sleeve of any given density. My sleeve by virtue of its ,minute .porosity and low :density throughout 4its wall thicknessadmits a reduction of thethickness ofthe wall of the sleeve withoutirnpairment of the ultimate .result as the wholedensityis and has beenrreducedbecause any relative loss of total insulating value is offset b ythe relative reduction in total .heat capacity-.of lthe sleeve. Similarly, when -my hot top ,is `employed with `smaller molds, .thinner sleeves S,.not necessarily directly proportionately thinner, may be employed in view of the `more rapid Asolidilicationrof the ingot. The `contrary-tends to follow for larger molds. Insum, Athe uniform porosity and low densitythroughoutthe wall tof-my` sleeve permits, andin part directs, me tochoose `theoptimumwall thickness of the sleeveatapproximately .the ,point of `balance between the best advantage owing from reducing ytotal heat-capacity and preserving totalyinsulation. This `is illustrated in the example of 4size and proportions given below and contributes, as I believe, materially-tto :the desirable results obtained. vI am not .unaware Yof-other factors contributing to the preservation `of heat in `the crop by the wall offfthe sleeve,such as the-colorof-the ware, the resistance of the skin-of ,the feed -opening 4to surface transfer of heat yand `the reectivefquality'ofuthe exterior surfaceofthe sleevein reducing radiationafactorspreserved in my lhot top .withtlight color and -smooth skin incident to my preferred methodoffmaking and burningthe ware. Consideration of \these lthermal lfactors as such is not intended toobscure the beneficence :of -the preferred proportion of .height .to diameter `of the feed opening within the sleeve .Whereina ydesirably high static head ofrnolten crop is-obtainable andpreservable fthrough the ultimate thermal efficiency of the sleeve which `defines the shape of thefeed opening.

My preference is that the collar C be made by extrusion of'wet clay alone, dried and 'burned in V orthodox fashion Wherewith to'havethe expected density of about 1.25 ounces 4'per cubic inch and the usual thermal and physical properties of well-made, dense, burned lire-clay products. For rule of thumb, the collar may have about twice the density and twice the heat capacity per unit of volume of the sleeve (not necessarily twice the unit strength since the minute cellular structure of the sleeve has strength disproportionate to its lightness) and a relatively low insulating value compared with the sleeve.

As suggested in the drawings, the sleeve S has a central right cylindrical opening, or so-called feed opening 1, which may be circular or polyangular or a mixture thereof, preferably tending generally toward circular to preserve strength and minimize surface area in respect to volume; the feed opening preferably being about 120%- 140% as long as its mean internal diameter, whereby to afford a substantially great static head of molten steel above the ingot when freshly filled as suggested in the right half of Figure 4. The opening 1 extends from end to. end of the sleeve S, and the inner surface of the sleeve, defining the opening, is, as I prefer, smooth, continuous, hard and noticeably resistant to fluid steel absorption or adhesion and tending to be self-preserving and heat reflecting when the opening is filled with molten steel. The wall 2 of the sleeve is thick, 2%" to 3, for a mold with an upper opening about two feet square, and of uniform thickness throughout, except for the extra thickness incident to external longitudinally extending ribs 3 which, however, are terminated equally spaced distances from the bottom of the sleeve whereby to rest on'the upper surface of the collar C, as at 4, and limit the telescopic entrance of the sleeve into the collar, Figures 3 and 4. The lower external surface of the sleeve S is smooth, continuous and cylindrical and of circular or quasi-circular form approximately corresponding to the shape of the feed opening. Preferably the lower outer corner of the sleeve S is chamfered as at S, Figure 5, to facilitate the application of a ceramic seal 6 between the sleeve and collar as will be more fully described below.

In this preferred form of my invention the volume of the feed opening 1 in the sleeve S is for rule of thumb about, and need not substantially exceed, 10% of the volume of the mold. Other factors bearing on the measurement of the actual volume and mass of the final crop and the accomplishment of the novel smallness thereof will more fully appear below, from which the preferred volume of the feed opening of the sleeve in relation to the mold and ingot can be more particularly stated. As a practical matter a sleeve for a successful hot top embodying my invention used with the above mentioned 2 square mold had wall thickness of about 2%", a mean internal diameter of about 15% and length of 211/2".

The collar C has a right cylindrical central opening, the circularity or quasi circularity of which corresponds to the lower exterior of the sleeve S and is telescopically receptive of the same, with as close a lit as is practicable with refractory products: I allow a nominal clearance 11, Figures 4 and 5, of about 3/8" between the inner surface of the collar and the outer surface of the sleeve in hot tops of about the size mentioned above. Externally the collar C has its side surfaces formed and dimensioned to enter the brim of the mold, Figure 4, with appropriately small clearance therefrom and has Short external supporting lugs overlying the top surface of the mold and supporting the collar in the mold as shown in Figure 4. In practice removable wedges 13 may be interposed between the lugs and the top face of the rnold in the first instance in the known and usual Way. The end surfaces of the collar as well as the end surfaces of the sleeve are cut normal to their axes and the ribs and lugs of the sleeve and collar are formed to locate the sleeve and collar coaxially of each other and coaxially of the mold when the assembled hot top, Figures 2 and 3, is placed in operative relation to the mold as shown in Figure 4. The wall of the collar C is of uniform thickness longitudinally and of variable thickness circumferentially, Figure 2, to accommodate the difference, whatever it may be, in shape between the brim of the mold and the sleeve. The minimum wall thickness of the collar is suicient to afford necessary structural strength for manufacture and use, but the greatest minimum thickness may respond to the preferred size and proportion of the sleeve and/ or hot top as a whole consistent with the entire teachings of the practice of my invention.

To form my whole hot top the lower end of the sleeve S is inserted in the collar C, Figures 2-4; the ribs 3 of the sleeve preferably preventing complete entrance of the sleeve to the full depth 0f the collar, Figure 4, and, pursuing the dimensional example mentioned above, the collar may have overall length, i. e. height as viewed in Figure 4, of about 9 and the sleeve may enter but about 7" wherewith the lower end of the sleeve stands about 2 higher in the mold than does the collar; thus exposing the lowermost end of the collar to contact with the molten steel when the ingot is first poured to the level L, Figure 4: a thing which I have found to be preferable in the practice of my invention and of apparent advantage toward obtaining the desirable results thereof. For example, the exposed lower end of the collar appears to tend to freeze and bond to the adjacent liquid steel more quickly and tends to anchor the whole hot top in the mold and aid in effecting the seal with the mold as at 14, Figure 4.

Before or after inserting the sleeve in the collar there are tied around the exterior of the sleeve a plurality of wire bands or hoops 7, Figures 3 and 4, and a band or hoop 15 is snugly secured around the collar under the lower ends of the lugs 12. The ribs 3 of the sleeve may be notched as at 8 to receive and locate the bands 7. After the parts are assembled they are firmly tied and secured together by up and down ties or tie wires 16 tautly drawn between one or more of the bands 7 and the band or hoop 15. The bands serve the additional function of preserving the hot top against deleterious fracture, or opening if fractured, pending the pouringz casting and/ or cooling of the ingot and crop. The ties 16 may be attached to the lugs 12 of the collar as well as or instead of to the band 15. In lieu of the up and down ties 16 the sleeve and collar may be bonded together with bonding material placed in the space 11 as described below.

With the sleeve and collarassembled and tied together, the hot top is preferably placed upsidedown and the seal 6 puttied, poured or troweled in at the chamfer 5 and more or less into the space 11 to seal the space 11 between the sleeve and the collar and prevent molten steel from entering that space or finding egress therethrough. The seal 6 may comprise a wet mixture of an aqueous solution of sodium silicate and brick dust or other nely divided and fired refractory, which while Wet is readily poured and/or troweled into the annular sealing place and space as shown in Figure 5, and after drying and setting, is resistant to spalling or other harmful deterioration upon contact with molten steel. Alternatively, the space 11, or much of it, above the seal 6 may first be filled with Portland cement to bond or integrate the sleeve and collar together, and the need for the ties 16 thus eliminated; the silicate mixture seal 6 preferably being applied after the cement thereabove has been poured or injected into the space 11 to prevent contact between the cement with molten steel and possible deleterious gasification from the cementto the ingot. For a second alternative, the sleeve and collar may be bonded together with high alumina cement poured or injected into the space 11, and I may use the same high alumina cement to substitute for the seal 6 because of the resistance of this cement to gasification. Should any bonding material, employed in the space 11 for its bonding virtue as such, tend to have any incompatability with the ingot or the casting thereof, my preferred silicate seal may always be interposed between the bond and the ingot as shown in Figure 5.

In fhe'practi and Operation 0f.'1111/5irwerltorrsthewhole.f hot top H is placed onandrin the of:themo ld. lvl.asvv shown in Figure `4.andnthe initialgpour--of-Ymolten steel.

made up toV `aboutthelevel L. Thelpo ng'isfthenirb` terrupted for.a minuteor; so (whileparrititial pour. may be made in a different mold), wedges v12A removed, and the first chilling orfreezing`ofthe1steel adjacentthemold surface and. nearlthe lower.end .ofthecollanC. al,lowed tov take place.v I have.observedthagthisinitial chillingy includes the formation at 14 of afrozen or sufficiently when the hot top. is, filledjf withmolten crop. tionally,y my observationsA lead medito believe that a rfreez-` ing or quasi freezing lof -moltensteel-and/ ora .bond takes place betweenthelowermost endo fthe..collar and the` ingot at or with the lower end.` surface 17.'of the. collarsN and probably to aklesserY degreefatand with part-ofthe; inside lower exposedsurface 18 of thelcollarv by virtue` of the small surfacefareaspexposed andsrnallmass in;

volved and the highheatcapaeityof thebottomA of the collar and the proximity yof thelower endliof the collar`` to the cold wall of the mold Contemporaneously, the.: level L of molten steel may contact the lower end of the;

sleeve S, but the lower heat capacity of theL lattergandits high insulating value tendsto-vresist4 and de lay,free;/;ingl

of thelsteel adjacent thereto. In all events, I have .found that after the short` conventionalhpause.in-thei pouring of ingot at the level L my hot topacquires a satisfactory anchorage to the ingot, suicient to resist harmful oating of the hot top whenpouring isresnrnel, andaethe. same time begins to preservetand maintainliquidity of.:

the steel and delay freezing thereof atand belo,w the sleeve S, i. e., in ornear the.y lowermost part ofthefcrop;y in or about the part 20 of the,.casting Awhich lies 4below the sleeve and above the level, ofthebottom of-the collar.

After the first pour and pause, asecond pouring ofy steel lills the sleeve about to the 1evelL` near the top `of the sleeve wherewith to provideiahigh head yand reservoir.

of molten steel to augment the lprevention of piping :and

segregation in theingot. Withmy hot top even though, the sleeve is of low density, the tying por; bonding. ofV

sleeve to the collar andthe anchorage of the lcollar in the mold holds the hot topfagainstharmful oating and leakage of molten crop therefromfr from-,the brim,ofV

the mold. Thus the moltenerop.-K. is preserved v in place, and the high insulatingvalue ,andlow heat capacity and other beneiicent features and/ or proportions ofthe sleeve and hot top keep the small steel content of.the.hottop molten or liuid long enoughso that noV more than 1A@ of the entire castingt comprising ingotV and crop needsto be,A

cropped to yield a pipe-freeand segregationrfree, useful ingot. To put it conservatively, I have reckoned the crop as comprising substantially alll the good metal, sponge and dross lying above the bottom level 17 of the collar including. the stepped part 20 of the casting. In the practice of my invention, howeventests have shown that the stepped bottom of the hot op .which includesthe vpart 20 of the casting appears to have lifted all the sponge of the crop well up-into the feed Vopening of the sleeve S and that much if not allrthenpart; 20is also substantially segregation-free. Thus some `or all ofthe part 20 need not necessarily be cropped off, and,v correspondingly,v my invention may be credited with requiringlessthan a 10% crop or, where 10% is cro} ped,affordingi avsubstantial.

buffer or safety factorof useful metal in so much of the. part 20 as is croppedoif.

With the above considerations in-mind, the internal volume of the whole hot top in -relatirontothe volume ofv the ingot and mold may lbepredicated thus: Since the` ultimate solidified cropY has all the piping, porosity and dross from which the ingotvhas been ,preserved thevolume of the frozen crop as it stands in the hot top? in relationl to the volume of the ingot will exceed 10% while its weightandrnass islessthan 10%. Since the level L of` thegcropindts molten state is prudentlyha few .inches-V lovwenthanthe top of the sleeve toprevent inadvertent. overow., and1spilling, another increment-.lof volume is conveniently added. Since part of1the.n`nal.,crop lies withinlthemoldJ thefwhole mold volume ist greater than.y thevolume: ofuuseful ingotcast therein.;l Arough balance v offthese Consi der ationsA suggests thatinthis; preferred form-,ofmy invention ,they internal Volume4 of ,the ,sleeve S may be approximately: othe volume.. of themold, whence Lthewhole I`internal volume` of the. hottopginclud inggthe` diametrically enlarged space 20will materially. exceed 1A@ Ithe volume, of,the.mold,.` Whenlhowever as the operator judiciously refrains from-.filling 'the hot top` to the extreme upper level thereof, the final., resulting. weight ofsolid metal requiredy to becropped may befand.y characteristically, is,` nomore jthan. 1750( the, weight of the.w whole casting.; a Iresult long sought andnow first obtained.

by `my invention.

While I have illustratedand describedpreferredforms. and practices of my inventiorl,,lIlpLOi/eluens:Illodications andgchanges therein willoccur to those skilledim theart without departing from thevprinciples andA suba. stance thereof, and I donot intend4 to be. limited in theI scope ofmy patentztothe, specilic.forms and examples herein specifically described, for the .sake lofillustration,-

andexpositon, nor in,any way-on manner ,inconsistent with the promotion of progress in-the an accomplished by my invention.l

I claim:

1. A ceramic hot top., for use..with `ingot tmolds. for. casting ingots comprising an inner substantially cylindrical burned yclay sleeve .portion open at both ends;.witl1.` a centralfeed opening and, adapted to be.y disposedbovev and coaxially ofthe mold, the Iwall `ofsaidsleeve portion being characterized by its substantially uniformporosity,

density and thickness, lowdensity, low heatlcapacity and;

high insulating value, hayinga .density 4of aboutya ounce peri-cubic inch-andV insulating valuehwhich under-steady!v heat conditions can .maintain aboutlOOO" F. at its.' inner surfacewithzabout, 200 F.` at its` outersurface, thel said I,opening nof* saidA sleeve portion having from about 10% to 50% greater height than lmean*transverset-di-A mension, said hot v,top also `comprising`-l-a .collar portion .l

formed ofdense, v strong burned claylwith'density ap proximately twice zthedensity ofsaid sleeve portionand with a centralcpening formed, complementalilyto theu exterior of the lower part of said sleevewportionand,

closely and freely receiving wand-encompassing( the lower part; of said sleeve portionand having a heightof ,bef`

tweenabout 1/3 to 41/2 the height ofsaidsleeve portiom and having an exterionformcomplementary tovthein-` terior of the upper end of the ingotmold andfadaptedfto;

be closely and freely disposed therein, means forsupporb,l ing said collar portion adjacent the brim ofqsaidmold with-rits lower part disposed belowlthebrim, means for holding ,said sleeveportion against substantial upward or downward motion relative `towsaid collar porjtionand` means for sealing Athe lower:y end offsaid sleeve .portiontin relationto said collar vportion against ash5or flowof uidvmetal upwardly therebetweenl whenthe.ingot is poured and said sleeve portion-is substantially filledwith fluid-metal, said hottop havingan internalivolume. of not more than about l10% of the :volume of the lngot and crop and said collar portion,havingstrengthvin shear and -resistanceto spalling where it is` externallyaengaged y per cubic inch and insulating value which under steady heat conditions can maintain about 1000 F. at its inner surface with about 200 F. at its outer surface, approximately half the volume of said wall comprising voided pores at least the greater part of which are not substantially larger than particles of talcum powder and all said pores having been fired internally by substantially complete combustion of carbonaceous material therein and at least the smaller of said voided pores being substantially free of ash, the said opening of said sleeve portion having from about to 50% greater height than mean transverse dimension, said hot top also comprising a collar portion formed of dense, strong burned clay with density approximately twice the density of said sleeve portion and with a central opening formed complementarily to the exterior of the lower part of said sleeve portion and closely and freely receiving and encompassing the lower part `of said sleeve portion and having a height of between about 1/3 to V2 the height of said sleeve portion and having an exterior form complementary to the interior of the upper end of the ingot mold and adapted to be closely and freely disposed therein, means for supporting said collar portion adjacent the brim of said mold with its lower part disposed below the brim, means for holding said sleeve portion against substantial upward or downward motion relative to said collar portion, and means for sealing the lower end of said sleeve portion in relation to said collar portion against flash or flow of uid metal upwardly therebetween when the ingot is poured and said sleeve portion is substantially iilled with fluid metal.

3. A -ceramic hot top for an ingot mold comprising a hollow cylindrical portion having an interna1 feed opening of volume of about 1A@ the volume of the mold and of length about 120% to 140% the mean diameter of the opening and having a wall surrounding said opening of thickness from about 37% to 1;@ the mean diameter of said opening; the wall being characterized by its uniformly minutely porous structure and lowdensity throughout its thickness and having between about and 60% uniformly distributed voided pores, at least of such pores being not substantially larger than a particle of talcum power and from none to 40% of such pores being not substantially larger than a grain of granulated table sugar, all said pores having been fired internally by combustion of carbonaceous material therein, substantially all said pores being free of unbumed carbonaceous material and at least the smaller of said pores being substantially free of ash, the density of said wall not substantially exceeding 0.7 ounce per cubic inch and said wall having insulating value sufficient to maintain but about 200 F. to 300 F. on its outside against about 900 F. to 1000 F. on its inside under steady heat conditions,

References Cited in the le of this patent UNITED STATES PATENTS 97 Wood Mar, 3, 1829 426,643 Lenderoth Apr. 29, 1890' 1,500,733 Howard July 8, 1924 1,508,931 Gathmann Sept. 16, 1924 1,650,700 Egler Nov. 29, 1927 1,692,491 Dumas Nov. 20, 1928 1,698,603 Moore Ian. 8, 1929 1,737,665 Messler Dec. 3, 1929 1,794,840 Egler Mar. 3, 1931 1,854,899 Goldschmidt Apr. 19, 1932 1,913,434 Dumas lune 13, 1933 1,938,170 Bellamy Dec. 5, 1933 2,263,437 Cameron Nov. 18, 1941 2,361,386 Eayrs Oct. 31, 1944 FOREIGN PATENTS 12,991 Great Britain May 15, 1897 485,507 Great Britain May 20, 1938 95,874 Sweden May 30, 1939 

